Existing secure transmission systems depend on encryption to prevent an interceptor from extracting information from a message. This typically requires a key, or code, known to both the transmitter and the receiver but unknown to the interceptor. Relatively high costs are associated with continual renewal of the code. There is also the possibility that past data can be compromised by subsequent loss of its code, or key. Other systems, predicated on lack of the interceptor's knowledge of the system structure, will inevitably be compromised eventually and may provide false security until the compromise is discovered.